When using rigid conduit nipples between safety switches or between safety switches and industrial control panels where only locknuts (inside/outside) are being used and the voltage is >250 VTG, is a grounding locknut required OR are safety switches listed for bonding using only standard locknuts ?
250.7 & Safety Switches
- Thread starter augie47
- Start date
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- Location
- Illinois
- Occupation
- retired electrician
You are fine as long as you have removed all of the knockout rings. If you are using a raceway that is smaller than the largest knockout ring, you need some type of bonding. As far as I know, the only knockouts that are listed for grounding without all of the rings removed are on boxes, not disconnects or panels.
Thanks. I'm afraid that was an "old-age" question that snuck in as a result of an inspection earlier today. 250.97 Exception (2) makes that clear.
We had been discussing 4" sq boxes with concentric KOs on 277v systems and the fact they most, if not all, are listed for use without extra bonding means and I had a brain fart.
- Location
- New Jersey
- Occupation
- Journeyman Electrician
I agree for boxes there's the listing option for concentric or eccentric KO's but for disconnect switches there is no such option so either the entire KO is removed or a bonding bushing would be needed. Now if one end of the raceway starts at a panel with a full sized KO and the disconnect switch has a eccentric, concentric or tangential KO (Square D) then is the bonding bushing still required at the disconnect switch if the raceway contains an EGC?
Cow
Senior Member
- Location
- Eastern Oregon
- Occupation
- Electrician
I contacted Siemens 6 months ago to ask them about their safety switches and whether the knockouts were rated for grounding/bonding. I was told they weren't and he went on to say about 7 years ago or so all the different disconnect switch manufacturers lost their ratings also.
I never contacted any other manufacturers to find out if that was true or not.
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